(Supported in part by NIH GM 45983 and AHA 93-3030G to M. Lennartz). We have demonstrated that arachidonic acid (AA) is required for phagocytosis to occur and that an apparently unique (phagocytic ) phospholipase (pPL) is responsible for AA release. Inhibition of pPl results in the accumulaiton of electron lucent vesicles (ELV) in the cytosol of human monocytes. The ELV do not label with cationized ferritin, suggesting they are not contiguous with the plasma membrane. Our goal is to use the HVEM to better visualize the morphology of the ELV in 3-D, and to quantify the number of vesicles that contain an immunogold label when the cells are incubated with BSA. Many stereo HVEM and IVEM images were recorded from 0.5 and 1.0 (m thick sections. The data clearly reveal that vesicles in questions are no continuous with the plasma membrane and do not appear to be connected in a network arrangement. Lennartz, M.R., A.F.C. Yuen, S. M. Masi, D.G Russell, K.F. Buttle and J.J. Smith. (1997) Phospholipase A2 inhibition results in sequestration of plasma membrane into electron lucent vesicles during IgG-mediated phagocytosis. J. Cell Sci., 110:2041-2052. DISSEMINATION AND TRAINING SUBPROJECTS